1. Field of the Invention
The present invention relates to an optical network, and more particularly, to a method of detecting a rogue ONU, and an OLT and PON system using the same.
2. Related Art
A cable, a fiber optic, and a broadband connecting technology such as wireless have been widely distributed. In a communication network between a subscriber and a service provider, it is difficult to provide reliable high-quality voice/video services.
A passive optical network (PON) system connects an optical network unit (ONU) and an optical line terminal (OLT) through an optical line in a point-to-multipoint connection manner.
The OLT, which is a source of the PON, is disposed in a central office of a service provider. Downstream from the OLT is transmitted to a plurality of ONUs.
The PON system uses time division multiplexing in order to transmit upstream from the ONU to the OLT. Each ONU transmits the upstream only within a defined time interval according to upstream bandwidth allocation transmitted by the OLT.
When the ONU terminal of any terminals does not transmit upstream according to the upstream bandwidth allocation within a specific time interval, the ONU terminal of other subscribers cannot normally communicate with the OLT. In this case, in order to search the malfunctioning subscriber ONU terminal, there is a problem of searching subscriber terminals distributed within several tens of kilometers one by one.
Further, an optical power splitter disposed in a remote node is a passive device equally dividing the optical power by the number of ports, which cannot serve to intercept abnormal upstream transmission.
The rogue ONU implies an ONU that hinders the upstream communication of other normal ONUs by not transmitting upstream within a specific time interval according to the upstream bandwidth allocation information transmitted by the OLT, as described above. Physically, the rogue ONU implies an ONU that does not turn-off transmission laser of an optical transceiver of the ONU according to the upstream bandwidth allocation information.
The ONU should transmit upstream only within the time interval allocated to the ONU. The rogue ONU may deteriorate services of the normal ONUs. Therefore, the detection of a rogue ONU is one of the important issues in the PON system.
Disclosed are various methods in order to detect the rogue ONU. There is proposed a method of detecting the received optical signals by adding a hardware device to a receiving end of the optical transceiver of the OLT. As another example, there is proposed a method of sequentially disabling an operation of the rogue ONU candidates in a software manner. However, according to these methods, it takes much time to detect the rogue ONU. In addition, after the detection of the rogue ONU is completed, it takes much time to return normal ONUs to normal operation.